This invention relates to an insertion element subject to thermal stress and wear, in particular a segment for the assembly of a dip tube which extends centrally from above into a refractory-lined cyclone separator of a cement clinker production line and can be suspended on the cyclone deck.
Installations for the production of cement clinker from cement raw meal include a rotary kiln and, connected upstream thereof as viewed from the material flow end, a cyclone suspension heat exchanger with a calcinator. In the cyclone suspension heat exchanger system, the cement raw meal is preheated in combined co-current/counter-current with the hot flue gas of the calcination stage or of the rotary kiln, and the material precalcined in the calcination stage is separated from the hot gas in the lowermost cyclone of the cyclone suspension heat exchanger system and fed into the rotary kiln. The hot-gas cyclones of the cyclone suspension heat exchanger train, in particular the lowermost cyclone, which comes into contact with hot gas and hot meal at a temperature of, for example, 700 to 950xc2x0 C., are naturally subject to severe mechanical, chemical and thermal stress and thus to severe thermochemical and abrasive wear. This applies especially to the dip tube extending centrally from above into the cyclone separator.
German patent document DE-C-32 28 902, issued May 27, 1987 to Klxc3x6ckner-Humboldt-Deutz AG for a Cyclone Separator, discloses a dip tube having a plurality of segments connected to one another in detachable fashion in order that individual dip tube segments can be renewed at a relatively low cost in time and effort in case of wear and deformations of the dip tube shell. It has already been suggested to fabricate the dip tube segments entirely from ceramic material, which, while it is heat-resistant, does not withstand more severe mechanical stresses. For this reason, dip tube segments are commonly fabricated from heat-resistant cast steel.
The casting of thin-walled dip tube segments, however, runs into limitations in that segments, if they are to be no thicker than approximately 15 mm, can be cast free of inhomogeneities only up to a length of approximately 120 cm. Large hot-gas cyclones, however, require correspondingly large dip tubes, in which the individual segments are to be well over 120 cm long and, for reasons having to do with installation, must not be too heavy.
It is an object of the invention to create an insertion element, in particular a segment for the assembly of a segmented dip tube subject to thermal stress and wear for a refractory-lined cyclone of a cement clinker production line, the individual insertion element being capable of being fabricated and installed with a length greater than 120 cm and distinguished by a long service life.
The heat-resistant and wear-resistant insertion element of this invention is a composite structure made up of a comparatively thin-walled and lightweight metallic carcass on which are arranged webs of a metallic lattice-like mesh. The lattice openings of the mesh are filled with a ceramic composition that is heat-resistant and wear-resistant with regard to mechanical and chemical actions. The heat-resistant ceramic composition is cast and/or injected and/or vibrated/vibratorily compacted and/or pressed into the lattice openings of the mesh, which may be elastic, for example, expanded metal mesh.
The heat-resistant ceramic composition is capable of flowing during the fabrication of the composite structure, and it may also be hardened by an additional heat treatment such as sintering, tempering, etc. The ceramic composition may include silicon carbide (SiC), and it may further include a hydraulic binder such as, for example, cement, which lends special strength to the ceramic composition after its hardens.
The integrated lattice mesh in the composite structure acts as reinforcement for the heat-resistant ceramic composition, which is intended to lie on the side subject to wear of the component assembled from the composite segments, and thus, in the case of the segmented cyclone dip tube, on the outside of the dip tube, which is severely stressed by the hot gas/solids suspension flowing into the cyclone.
In order that the surface of the composite insertion element has the smallest possible porosity, the surface of the ceramic composition and/or of the outside of the metallic carcass is provided with a heat resisting sealing coating, in particular glazing, glaze, enamel, and the like.